What about a PC sound card?
________________________________ From: Alexander Pummer <alex...@ieee.org> To: Discussion of precise time and frequency measurement <time-nuts@febo.com> Sent: Thursday, August 7, 2014 5:06 PM Subject: Re: [time-nuts] Low noise powersupplies to measure a power supply noise, better to say the noise spectrum, you would need a very large non polarized capacitor and spectrum analyzer, The input of the spectrum analyzer does not like DC, and has low impedance. Since spectrum analyzer's input impedance is usually 50 ohm, for to be able to see the noise at low frequency you need C = 1/( 2 x 3.14 x 50 ohm x f Hz ) capacitor, and you would need a DC level limiter to prevent blowing the input of the spectrum analyzer during the charge up of that capacitor. If you could get a hold of an old HP 1Meg to 50ohm buffer amplifier you would need much lover capacitance or if the buffer has AC input capability with low enough corner frequency like the Tektronix P6201 FET probe, you would not need any capacitor. And that would make your life much nicer since capacitors could generate noise to.. Charles Wenzel in his circuit collection files ha very nice good working noise reduction circuits. 73 Alex KJ6UHN _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.